Plastic materials have low thermal resistance and flame resistance compared to metal or ceramic materials, but they have advantages such as lightness, design flexibility, and moldability, and thus are widely used in materials for a variety of products, from household items to industrial areas including automobiles and electrical and electronic products.
There are various types of plastic materials, from commodity plastics to engineering plastics that are widely used in areas that need various functions and performance characteristics.
Of these plastic materials, polyphenylene ether resin has excellent electrical and mechanical properties, and also a high heat deflection temperature. Thus, polyphenylene ether resins are widely used as engineering plastic materials in various areas.
Polyphenylene ether resin was developed by General Electric Co. in the USA. Based on its excellent thermal resistance, polyphenylene ether resin is becoming a useful industrial material that is mainly used as a blend with high impact polystyrene. More recently, polyphenylene ether resin is being employed in the form of alloys such as polyamide/polyphenylene ether resin alloys compatibilized by a reactive extrusion method, that is, a method for compatibilizing an incompatible blend, and polypropylene/polyphenylene ether resin alloys prepared by adding a compatibilizer as a third substance.
Disadvantages of polyamide/polyphenylene ether resin alloys have been compensated for effectively, so that the alloys can have a good balance of thermal resistance, impact resistance, and chemical resistance. Thus, polyamide/polyphenylene ether resin alloys are being employed in automobile components such as wheel caps, junction boxes, and under-the-hood components.
Recently, there has been a need for materials that can be used in plastic exterior components by electrostatic online painting simultaneously with other metal material components. See, for example, EP 685527 B1 to General Electric Co., directed to an electroconductive polyamide/polyphenylene ether resin alloy used in automobile fender components.
Development of a polyamide/polyphenylene ether resin alloys having electroconductivity enabled electrostatic painting to be performed simultaneously with other metal components, without a need for an additional painting process, thus saving production costs.
As a way to embody electroconductivity in polyamide/polyphenylene ether resin alloys, a method of adding an electroconductive filler such as carbon fiber or carbon black was proposed. See, for example, JP H04-300956 A. However, carbon fiber deteriorates the moldability of products, and when using a conventional carbon black, carbon black has to be added in large amounts in order to achieve the electroconductivity necessary for application to electrostatic painting. Either case may result in insufficient impact resistance and moldability.
To resolve this problem of impact resistance and moldability, a nano unit carbon fiber (carbon fibril) and electroconductive carbon black with an adjusted size have been used, but there occurred a problem of reduced compatibility between polyamide and polyphenylene ether. See, for example, JP 2756548 B2.
To resolve the aforementioned problem of reduced compatibility while producing a polyamide/polyphenylene ether resin alloy having excellent properties, it is important that a compatibilization reaction proceeds smoothly between polyphenylene ether, polyamide, and a compatibilizer.
In this regard, a conventional method of compatibilizing polyamide and polyphenylene ether first, and then adding an electroconductive carbon black therein was disclosed. See, for example, EP 685527 B1.
However, according to this method, polyamide/polyphenylene ether resin alloy, compatibilizer and other additives must be added in a particular adding order using a special extrusion processing equipment with a plurality of side feeders installed therein. This is uneconomical due to high investment costs, and further, the restrictive order of adding the materials decreases productivity.
Furthermore, methods of using nano size carbon fibril or carbon black have been proposed, but these methods have yet to be optimized to provide electroconductivity effectively.
Therefore, the electroconductive fillers used in conventional polyamide/polyphenylene ether resin alloys are still a problem in terms of properties and economic feasibility. Thus, there is a need to improve the efficiency of electroconductivity and to reduce the amount of electroconductive filler that should be added.